Firebox boiler with reduced temperature variation

ABSTRACT

A boiler firebox comprises arcuate front and rear end water walls connected respectively to front and rear ends of right and left side water walls. The end walls curve outward from respective ends of one side water wall and then inward to the respective ends of the other side water wall. The end and side water walls enclose a combustion chamber, and are connected at ends thereof such that water can circulate through the end and side water walls. Water input ports can be provided in water walls on opposite sides or ends of the firebox such that the flow of circulating water can be divided with about half entering the water wall on one side or end of the boiler and the other half entering on an opposite side or end, thereby reducing temperature variations in water near the input ports compared to boilers with a single input port.

This invention is in the field of firebox boilers and in particular such boilers where the firebox is enclosed in hollow water walls that are filled with water or like boiler liquid.

BACKGROUND

Firebox boilers typically comprise a firebox containing one or more burners fueled by coal, natural gas, fuel oil, or the like. A boiler shell, also referred to as a boiler drum, is mounted above the firebox and contains water or a like boiler liquid such as a mixture of glycol and water. Fire-tubes are mounted inside the boiler shell and extend substantially horizontally from one end of the boiler shell to the other, and hot combustion gases from the firebox pass through the fire-tubes to an exhaust.

In a three pass fire-tube boiler, for example, the combustion gases rise from the burner to the top of the firebox and along under the boiler shell to a rear end of the boiler shell where they enter a lower set of fire-tubes, and pass through the boiler shell to a turn around chamber on the front end of the boiler shell where the combustion gases then enter an upper set of fire-tubes and pass through the boiler shell again to an exhaust chamber on the rear end of the boiler shell, and then out through an exhaust stack. Thus the combustion gases pass the boiler shell three times before being exhausted—once under the boiler shell, then through the boiler shell from rear end to front end, then back from front end to rear end. On each pass, heat is transferred from the hot combustion gases to the water in the boiler shell.

Other configurations of such boilers are also well known where the combustion gases pass through the boiler various numbers of times along various paths.

In order to draw more heat from the combustion gases, it is further well known to enclose the firebox with hollow walls filled with water, commonly referred to as water walls, comprising an inner wall and an outer wall with a space between them. Holes are provided between the top of the water walls and the boiler shell such that water circulates between the water walls and the boiler shell. Typically, such boilers are connected to pipes for heat distribution, with hot water or steam exiting the boiler shell through a pipe connected at a top end thereof, and returning as water or condensate through a pipe connected at a bottom of one of the water walls.

Typically, the firebox is a rectangular shape with side water walls extending from the front end to the rear end along each side, and front and rear end water walls extending from one side to the other to enclose the firebox and form a combustion chamber. The inner and outer walls are typically relatively flat plates, and so stay bolts pass through the water walls to secure the inner and outer walls together when the water is pressurized during operation of the boiler. The spacing of the stay bolts will depend on the contemplated operating pressure of the boiler, but in a typical water wall a significant number of stay bolts is required.

Firebox boilers with water walls are disclosed for example in U.S. Pat. Nos. 134,284 to Huntington, 262,976 to O'Brien, and 539,844 to Wilson. The boilers of Huntington and Wilson illustrate boilers where the water walls enclose the bottom of the firebox as well as the sides and ends. The early steam boiler disclosed by O'Brien shows water walls along each side curving toward each other at the rear end, however the water walls do not enclose the firebox on the front end, or meet at the rear end. The water walls in O'Brien act only as a heater for feed water entering the boiler shell, and a check valve prevents water from moving out of the boiler shell back into the water walls.

A problem with such conventional boilers is that the rectangular shape of the firebox results in corners that are farther from the burner than the side and end walls. Water in the corners thus is heated more slowly than in the closer portions of the water walls resulting in uneven temperatures that create stresses that lead to structural failure. Uneven heat transfer to the water also reduces efficiency in steam boilers, as all water must reach the same temperature in order to satisfactorily produce steam. When operating as a water boiler, circulation in the water walls is impeded because of the corners, leading to stresses due to uneven temperatures that can cause cracking in the corners, or stay bolt failures.

U.S. Pat. No. 626,118 to White recognizes the problem in the corners of the water walls, and rounds the corners of the outer wall to add strength. Japanese Patent 06221508 to Suehiro Tomio provides an expanded corner to absorb thermal stress.

Conventionally, the stay bolts connecting the inner and outer walls of water walls are subject to corrosion and failure. U.S. Pat. No. 1,808,488 to Baker provides convex side and end water walls that curve outward at the bottom and then back inward at the top to provide structural strength and avoid the necessity of providing stay bolts between the inner and outer walls. The side and end water walls meet at conventional square corners where they are connected by a port through the respective walls to allow circulation.

Vertical cylindrical fireboxes with horizontal fire-tubes are also known, however are limited in capacity since the length of the fire-tubes, and thus the length of each pass through the boiler shell is limited. The boiler shell could be extended beyond the walls of the cylindrical firebox to increase the length of the fire-tubes however such a configuration results in uneven heating of the portion of the boiler shell that is not directly over the firebox, and thus leads to further problems associated with stress and circulation.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a boiler firebox that overcomes problems in the prior art.

The present invention provides in one embodiment, a boiler firebox comprising right and left side water walls. An arcuate front end water wall is connected to a front end of the right side water wall and is connected to a front end of the left side water wall, and curves outward from the front end of the right side water wall and then inward to the front end of the left side water wall. An arcuate rear end water wall is connected to a rear end of the right side water wall and connected to a rear end of the left side water wall, and curves rearward from the rear end of the right side water wall and then forward to the rear end of the left side water wall. The end and side water walls enclose a combustion chamber, and are connected at ends thereof such that water can circulate through the end and side water walls.

In a second embodiment the invention provides a boiler comprising a firebox with right and left side water walls and front and rear end water walls enclosing a combustion chamber, and connected at ends thereof such that water can circulate through the end and side water walls. A boiler shell is mounted above the firebox such that the boiler shell is in fluid communication with the side and end water walls and such that water in the boiler shell is heated by a burner in the firebox. An output port is operatively connected to the boiler shell, a first water input port is provided adjacent to a bottom of a central portion of a first water wall, and a second water input port is provided adjacent to a bottom of a central portion of an opposite second water wall. Circulating water flows out of the boiler through the output port, through a distribution network and back into the boiler through the first and second water input ports.

In a third embodiment the invention provides a boiler firebox comprising a right side water wall comprising an right inner wall and a right outer wall and a left side water wall comprising an left inner wall and a left outer wall. A front end water wall comprises an arcuate front inner wall connected to a front end of the right inner wall and connected to a front end of the left inner wall, and curving outward from the front end of the right inner wall and then inward and connected to the front end of the left inner wall, and a front outer wall connected to the front end of the right outer wall and to the front end of the left outer wall. A rear end water wall comprises an arcuate rear inner wall connected to a rear end of the right inner wall and connected to a rear end of the left inner wall, and curving outward from the rear end of the right inner wall and then inward and connected to the rear end of the left inner wall, and a rear outer wall connected to the rear end of the right outer wall and to the rear end of the left outer wall. The right, left, front, and rear inner walls enclose a combustion chamber, and water can circulate through a water chamber formed between the inner and outer walls of the end and side water walls.

Curving the end walls eliminates corners that are present in conventional firebox boilers, and thereby reduces the circulation and stress problems associated with such corners. The curved end walls further provide structural strength so that the number of stay bolts can be reduced, thereby reducing the problems associated therewith. A semi-circular arcuate shape provides a smooth transition between end and side walls for improved water circulation, and also provides significant structural strength.

Providing two input ports for circulating water reduces the amount of cooler water entering at each input port, and thus reduces the temperature variation in water in the water chamber near the input ports, and so reduces stress caused by temperature variations.

DESCRIPTION OF THE DRAWINGS

While the invention is claimed in the concluding portions hereof, preferred embodiments are provided in the accompanying detailed description which may be best understood in conjunction with the accompanying diagrams where like parts in each of the several diagrams are labeled with like numbers, and where:

FIG. 1 is a top view of a boiler of the present invention;

FIG. 2 is a schematic cross-sectional front view of the boiler of FIG. 1;

FIG. 3 is a schematic cross-sectional side view of the boiler of FIG. 1;

FIG. 4 is a top view of a boiler of the prior art;

FIG. 5 is a schematic cross-sectional front view of the prior art boiler of FIG. 4;

FIG. 6 is a schematic cross-sectional side view of the prior art boiler of FIG. 4;

FIG. 7 is schematic top view of an alternate embodiment of a firebox of the present invention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

FIGS. 1-3 illustrate a firebox boiler 1 of the present invention. FIGS. 4-6 illustrate a conventional firebox boiler 1P of the prior art.

The boiler of the present invention illustrated in FIGS. 1-3 comprises a firebox 2 formed from side water walls 4 and end water walls 6 enclosing a combustion chamber 8. The side and end water walls 4, 6 each comprise an inner wall 10 and an outer wall 12. The inner walls 10 of the side and end water walls 4, 6 are connected at corresponding ends thereof, and the outer walls 12 of the side and end water walls 4, 6 are connected at corresponding ends thereof such that a water chamber 14 is formed between the inner walls 10 and outer walls 12. The inner and outer walls 10, 12 are connected together by stay bolts 11 through the water chamber 14.

In the firebox 2 of FIGS. 1-3, the front end water wall 6F is vertical and arcuate. The front end water wall 6F curves outward from the front end of the right side water wall 4R and then inward to the front end of the left side water wall 4L. Similarly the rear end water wall 6R is vertical and arcuate, curving outward from the rear end of the right side water wall 4R and then inward to the rear end of the left side water wall 4L. Curving the end water walls 6 reduces the variation in the distance between the water in the water chamber 14 and the burner 16 in the firebox 2 compared to the conventional firebox 2P in FIG. 4.

In the conventional firebox 2P of FIG. 4, the ends of the side and end water walls 4P, 6P meet at a right angle corner 5P, and the water in the corner 5P of the water chamber 14P is therefore significantly farther from the burner 16P than the water at mid points of the water walls 4P, 6P. Uneven heating is thus significantly reduced, as are the associated problems of poor circulation and structural stress at the corners.

For the same length and width of firebox, because the side and end water walls the firebox 2 of FIG. 1 do not extend into the corners as they do in the prior art firebox 2P, the firebox 2 of FIG. 1 will have a somewhat smaller heating surface than the conventional firebox 2P of FIG. 4. Because the inner walls 10 of the firebox 2 are closer to the burner 16 however, more heat is transferred from the combustion gases to the water than is the case in the prior art firebox 2P, and so the efficiency of the firebox 2 of the invention is typically greater than that of the prior art firebox 2P.

The curved shape also provides increased structural strength to the end water walls 6 compared to the flat end water walls 6P, such that it is contemplated that the number of stay bolts connecting the inner and outer walls 10, 12 can be reduced, and the problems associated with failure of stay bolts can thereby be reduced as well.

While it is contemplated that other arcuate shapes will provide beneficial results, in the illustrated arcuate end water walls 6, the walls 6 are curved or arced to form one half of a circle, or a semi-circle, such that the inner and outer walls 10, 12 of the end water walls 6 meet the corresponding inner and outer walls 10, 12 of the side water walls 4 tangentially and curve in a constant radius from one side to the other. The semi-circular shape of the end water walls 6 provides a smooth and unrestricted circulation path around the water chamber 14, improving water circulation such that temperature variances in the water are further reduced. The semi-circular shape provides significant structural strength to the end water walls 6 as well.

A boiler shell 18 is mounted above a front portion of the firebox 2 and in fluid communication with the side and end water walls 4, 6 through circulation ports 20 and water channel 22 between the top of the rear end water wall 6R and the rear face of the boiler shell 18. The boiler shell 18 forms a top wall of the front portion of the firebox 2, and a lower rear face 24 of boiler shell 18 is exposed to a rear portion of the firebox 2.

A plurality of fire-tubes 26 extends horizontally from the lower rear face 24 through the boiler shell 18 to a front face 28 of the boiler shell 18. The illustrated boiler 1 is a three pass boiler including a turn around chamber 30 at the front end of the boiler shell 18 and a second upper set of fire-tubes 26 extending from the front face 28 of the boiler shell to an upper rear face 32. Combustion gases from the burner 16 thus pass under the boiler shell 18 to the rear face 24 thereof, through the lower fire-tubes 26 into the turn around chamber 30, and from there through the upper fire-tubes 26 to an exhaust chamber 36 at the upper rear face 32 of the boiler shell 18, and then out through a stack 36.

The water channel 22 between the top of the rear end water wall 6R and the rear face of the boiler shell 18 is formed by a upper and lower transition plates 40, 42. The lower transition plate 42 joins a top end of the inner wall 10 of the rear water wall 6R to a top of the lower rear face 24 of the boiler shell 28, and the upper transition plate 40 joins a top end of the outer wall 12 of the rear water wall 6R to the boiler shell 18 above the lower transition plate 42. The water channel 22 allows water to flow between the water chamber 14 in the rear water wall 6R and the boiler shell 18.

In the firebox boiler of the prior art as seen in FIGS. 5 and 6 there is a horizontal flat area 41P in the lower transition plate 42P where scale and like deposits that precipitate out of the water in the boiler gather and interfere with circulation through the water channel 22. In the illustrated embodiment of the boiler of the present invention, the lower transition plate 42 is curved both from side-to-side, as seen in FIG. 2, and from front to back as seen in FIG. 3 such that material deposited on a top surface thereof tends to slide off and fall to a bottom of the water chamber 14, improving circulation through the water channel 22, and reducing the need to shut down the boiler and clean out the water channel 22.

In hot water boilers of the prior art, as seen in FIGS. 1 and 3, circulating water enters the water walls at a single input port 50P in a lower portion of one of the water walls, shown as end wall 6P. The full flow of the generally cooler water returning from a distribution network is concentrated at one point in the water chamber formed by the water walls. This concentration of cooler water reduces the temperature of the water in the water chamber 14P near the single input port 50P, again causing temperature variations that cause stress on the water wall 6P and stay bolts near where the cooler liquid enters.

In order to reduce temperature variations, the present invention provides a first water input port 50A adjacent to a bottom of a central portion of one water wall and a second water input port 50B adjacent to a bottom of a central portion of an opposite water wall. Thus the ports 50A, 50B are located either on opposite end walls 6 or opposite side walls 4 and are connected by conduits to first and second ports of a T-connector 52. In operation, circulating water flows out of the boiler 1 through an output port 54, through a distribution network and back into the T-connector 52 where the flow divides with about half the flow entering one end of the boiler 1 through the first water input port 50A and half entering the opposite end of the boiler 1 through the second water input port 50B. Thus the temperature variation in the water in the water chamber 14 near the first and second water input ports 50A, 50B is reduced since only one half the volume of cooler water is entering each port.

FIG. 7 illustrates an alternate embodiment of a firebox 102 of the present invention. The inner walls 110 of the side and end water walls 104, 106 are arcuate, and as illustrated are semi-circular, bringing the heating surface in the corners closer to the burner 116, and increasing heat transfer to the water in the water chamber 114. The outer walls 112 of the side and end water walls 104, 106 are conventionally rectangular, as may be desirable for some applications. Temperature variations and associated stresses are reduced compared to the prior art firebox of FIGS. 4-6, however will be greater than in the embodiment of FIGS. 1-3.

Thus the foregoing is considered as illustrative only of the principles of the invention. Further, since numerous changes and modifications will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and accordingly, all such suitable changes or modifications in structure or operation which may be resorted to are intended to fall within the scope of the claimed invention. 

1. A boiler firebox comprising: right and left side water walls; front and rear end water walls connected to corresponding front and rear ends of the right and left side water walls to enclose a combustion chamber, and such that water can circulate around the combustion chamber through the end and side water walls; and wherein at least one of the front and rear end water walls is arcuate, curving outward from the a corresponding end of the right side water wall and then inward to a corresponding end of the left side water wall.
 2. The firebox of claim 1 wherein the at least one arcuate end water walls is substantially vertical.
 3. The firebox of claim 2 wherein the at least one arcuate end water wall is semi-circular.
 4. The firebox of claim 1 wherein the end and side water walls each comprise an inner wall and an outer wall, and wherein inner walls of the end and side water walls are connected at ends thereof, and outer walls of the end and side water walls are connected at ends thereof such that a water chamber is formed between the inner and outer walls of the end and side water walls.
 5. The firebox of claim 1 further comprising a first water input port adjacent to a bottom of a central portion of a first water wall, and a second water input port adjacent to a bottom of a central portion of an opposite second water wall.
 6. The firebox of claim 5 further comprising a first conduit connected to the first water input port at one end thereof and to a first port of a T-connector at an opposite end thereof, and a second conduit connected to the second water input port at one end thereof and to a second port of a T-connector at an opposite end thereof, such that a circulating conduit can be connected to a third port of the T-connector such that circulating water can enter the water walls through the first and second water input ports.
 7. The firebox of claim 6 wherein the first and second water walls are end water walls, and wherein circulating water can be connected to enter the water walls at opposite ends of the firebox.
 8. The firebox of claim 6 wherein the first and second water walls are side water walls, and wherein circulating water can be connected to enter the water walls at opposite sides of the firebox.
 9. A boiler apparatus comprising: a firebox according to claim 4; a boiler shell mounted above a front portion of the firebox such that the boiler shell is in fluid communication with the side and end water walls and such that the boiler shell forms a top wall of the front portion of the firebox, and a lower rear face of boiler shell is exposed to a rear portion of the firebox; a lower transition plate joining a top end of the inner wall of the rear water wall to a top of the lower rear face of the boiler shell to form a top wall of the rear portion of the firebox; an upper transition plate joining a top end of the outer wall of the rear water wall to the boiler shell above the lower transition plate, the upper and lower transition plates forming a channel to allow water to flow between the rear water wall and the boiler shell; a plurality of fire-tubes extending substantially horizontally from the lower rear face through the boiler shell to a front face of the boiler shell; wherein the lower transition plate is curved such that material deposited on a top surface of the lower transition plate tends to slide off the top surface of the lower transition plate and fall to a bottom of the water chamber.
 10. The apparatus of claim 9 further comprising a first water input port adjacent to a bottom of a central portion of a first water wall and connected to a first port of a T-connector, and a second water input port adjacent to a bottom of a central portion of an opposite second water wall and connected to a second port of a T-connector, and a circulating conduit connected to a third port of the T-connector such that circulating water can enter the water chamber through the first and second water input ports.
 11. A boiler comprising: a firebox comprising right and left side water walls and front and rear end water walls enclosing a combustion chamber, and connected at ends thereof such that water can circulate through the end and side water walls; a boiler shell mounted above the firebox such that the boiler shell is in fluid communication with the side and end water walls and such that water in the boiler shell is heated by a burner in the firebox; an output port operatively connected to the boiler shell; a first water input port adjacent to a bottom of a central portion of a first water wall and a second water input port adjacent to a bottom of a central portion of an opposite second water wall; wherein circulating water flows out of the boiler through the output port, through a distribution network and back into the boiler through the first and second water input ports.
 12. The boiler of claim 11 wherein the first and second water walls are end water walls, and wherein circulating water enters the boiler at opposite ends of the firebox.
 13. The boiler of claim 11 wherein the first and second water walls are side water walls, and wherein circulating water enters the boiler at opposite sides of the firebox.
 14. The boiler of claim 11 wherein the end and side water walls each comprise an inner wall and an outer wall, and wherein inner walls of the end and side water walls are connected at ends thereof, and outer walls of the end and side water walls are connected at ends thereof such that a water chamber is formed between the inner and outer walls of the end and side water walls.
 15. The boiler of claim 11 comprising a first conduit connected to the first water input port at one end thereof and to a first port of a T-connector at an opposite end thereof, and a second conduit connected to the second water input port at one end thereof and to a second port of a T-connector at an opposite end thereof, and a circulating conduit connected to a third port of the T-connector at one end thereof and to the distribution network at an opposite end thereof.
 16. The boiler of claim 11 comprising: an arcuate front end water wall connected to a front end of the right side water wall and connected to a front end of the left side water wall, and curving outward from the front end of the right side water wall and then inward to the front end of the left side water wall; and an arcuate rear end water wall connected to a rear end of the right side water wall and connected to a rear end of the left side water wall, and curving rearward from the rear end of the right side water wall and then forward to the rear end of the left side water wall.
 17. The boiler of claim 16 wherein the arcuate front and rear end water walls are substantially vertical.
 18. The boiler of claim 17 wherein at least one of the front end water wall and the rear end water wall is semi-circular.
 19. A boiler firebox comprising: a right side water wall comprising an right inner wall and a right outer wall; a left side water wall comprising an left inner wall and a left outer wall; a front end water wall comprising an arcuate front inner wall connected to a front end of the right inner wall and connected to a front end of the left inner wall, and curving outward from the front end of the right inner wall and then inward and connected to the front end of the left inner wall, and a front outer wall connected to the front end of the right outer wall and to the front end of the left outer wall; a rear end water wall comprising an arcuate rear inner wall connected to a rear end of the right inner wall and connected to a rear end of the left inner wall, and curving outward from the rear end of the right inner wall and then inward and connected to the rear end of the left inner wall, and a rear outer wall connected to the rear end of the right outer wall and to the rear end of the left outer wall; wherein the right, left, front, and rear inner walls enclose a combustion chamber, and wherein water can circulate through a water chamber formed between the inner and outer walls of the end and side water walls.
 20. The firebox of claim 19 wherein the arcuate front and rear inner walls are substantially vertical.
 21. The firebox of claim 20 wherein at least one of the front inner wall and the rear inner wall is semi-circular. 